(1) Field of the Invention
The present invention relates to a substrate storage container for use in storage, transportation, preservation, processing, etc., of substrates such as, for example silicon wafers, glass, glass masks, etc.
(2) Description of the Prior Art
Recently, in order to further enhance the productivity in the semiconductor industry, large-diametric substrates such as silicon wafers, glass wafers having a diameter of 300 mm have started to be used. Because any of such substrates is liable to sag due to gravity even if it is supported either lengthwise or crosswise, it is strongly demanded that (1) they should be handled securely by being stored in a predetermined substrate storage container so as not to be broken and (2) they should be isolated from particles and organic substances or prevented from being contaminated by metal ions etc., during transportation or during preservation.
A substrate storage container of this type is composed of, though not illustrated, a container body for holding a plurality of substrates in alignment, a door element for opening and closing the front opening of the container body and a sealing gasket interposed between the container body and the door element for creating a seal (see Patent literature 1: Japanese Patent Application Laid-open 2000-306988 (see FIGS. 1 to 10)).
The container body is a molding of a front open box type, formed of a transparent resin or the like, and is used for in-line transportation and preservation. Flanges for transportation are provided as appropriate on the top, bottom and/or side walls of this container body, so that the substrate storage container can be lifted up or transported along the processing line at high speeds overhead with these flanges engaged by robots and transporters. A window for monitoring substrates is partly formed on the rear side etc., of the container body while a plurality of supporting ribs for supporting substrates at their peripheral edge are arrayed vertically (see Patent literature 2: Japanese Patent Application Laid-open Hei 10-70185 (see FIGS. 12, 14 and 17)).
The door element is formed in correspondence with the front of the container body, has a front retainer attached to the inner surface (rear side) facing the container body for holding individual substrates at their front periphery, and is fitted to, and removed from, the container body by a robot. The front retainer is formed of a material being more flexible than that of the supporting ribs, and the contact part with substrates is formed with a multiple number of holding grooves arrayed vertically at regular intervals.
Each holding groove has an approximately U-shaped or approximately V-shaped section, and is formed so that the mid height of the groove is set at a position higher than the position at which the supporting ribs holds the substrate. That is, this configuration provides the function of marginally raising the substrates from the supporting ribs when the door element is closed, whereby contact friction between the substrates and supporting ribs can be reduced and the substrates can be prevented from being contaminated with abraded particles.
In the substrate storage container of this configuration, when the door element is removed from the container body, substrates are inserted along the supporting ribs into the container body or conversely substrates are taken out from the supporting ribs of the container body.
The conventional substrate storage container is configured as described heretofore, and they are transported at high speeds overhead by robot. However, the overhead transport system is difficult to control and high in cost and has a shortcoming that only a small amount of load can be transported at a time. Further, since the installation of overhead transport needs extra space in the height dimension, it is difficult to install it in a factory with a low ceiling.
In view of these circumstances, in recent years, techniques for transporting the substrate storage containers using inexpensive conveyors have been proposed and have started to be put into practical use. The conveyor transport, however, entails a drawback that the substrates and the supporting ribs are rubbed against each other due to vibrations during conveyance, causing substrate contamination, which is a new, considerable problem. Particularly, in conveyor transport, there is more than a small possibility that at the joint between one conveyor and another, the bottom of the substrate storage container might collide with the rail portion of the conveyors and run on the track, whereby the substrates and the supporting ribs are rubbed against each other due to vibrations, contaminating the substrates. Further, if a strong impact acts on the storage container during transport, the substrates will be brought into rigorous contact with the interior, backside of the container body, resulting in damage or breakage.
To solve the above problems, a method has been proposed, in which small projections that come into point or line contact with the undersurface of the substrate are formed on the top surface of the supporting ribs so as to reduce the contact area. However, when the projection comes into point contact with the substrate, the load of the substrate concentrates on the single point, so that there is a fear of the substrate being easily damaged. Further, since these projections are minute in size, there is the problem that imperfect filling and hence shrink marks and deformation are apt to occur during molding, producing variation in the height at which the substrates are supported. Moreover, since it is difficult to finely adjust the height of the projections, there are problems that the substrates cannot be supported horizontally and that failures to unload the substrate are liable to occur due to variation in the pitch distance.
The present invention has been devised in view of the above, it is therefore an object of the present invention to provide a substrate storage container wherein it is possible to prevent the substrates from being contaminated as a result of abrasion between substrates and supporting ribs due to vibrations etc., occurring during conveyor transport and it is possible to prevent the substrates from being damaged or broken by strong contact of the substrates against the container body even when a large impact is applied during conveyor transport, for example.